All Things Mk5 > How to Guides / Troubleshooting

Golf Gti mk5 DSG - Has Mayo in Expansion tank? something to worry about?

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ricky:
Hi Everyone,
I recently purchased a Gold GTI Mk5 DSG.
car has fsh and maintained well.
Only thing is recently i checked the expansion tank and it has mayo residue in there.
I know mechanic told me that unless you see it on the dipstick or the oil cap then it is just condensation build up.
Is this correct or is there something else much worse?
Appreciate any help and advise!

LC5F:
For oil in coolant, normally the usual suspect is head gasket, but the ones on TFSI's are meant to be bulletproof...

I would say the most likely suspect would be one of the oil to coolant heat exchangers -one of them may have started to let go, pushing oil into your coolant.

The issue you have is there are 2 oil coolers -one on the engine and also the DSG box - it could be either.
Pretty hard to diagnose with the cooler in the car, it will need removal and pressure testing to confirm failure.
Also your coolant system will need cleaning to get the oil out.

At a guess I would say engine cooler - BTW you are unlucky, it is not that common for them to fail.

Octoparrot:

--- Quote from: LC5F on September 10, 2020, 06:43:25 pm ---For oil in coolant, normally the usual suspect is head gasket, but the ones on TFSI's are meant to be bulletproof...

I would say the most likely suspect would be one of the oil to coolant heat exchangers -one of them may have started to let go, pushing oil into your coolant.

The issue you have is there are 2 oil coolers -one on the engine and also the DSG box - it could be either.
Pretty hard to diagnose with the cooler in the car, it will need removal and pressure testing to confirm failure.

Also your coolant system will need cleaning to get the oil out.

At a guess I would say engine cooler - BTW you are unlucky, it is not that common for them to fail.

--- End quote ---

I agree with this, also I'd say the opposite of what your mechanic said, its normal for these engines to have a bit of mayo under filler cap or on the dipstick if used on short journeys.

Stupots:
I agree with both previous replies... plus, go for the cheapest option first, which is the engine oil cooler anyway.

If it's the same as an Audi TT (my girlfriends) then it's attached to the oil filter housing. Her's also got mayo/oil in the coolant which first appeared in the expansion tank following a timing belt and water pump change. Reading on various VWAG forums suggested it wasn't unusual for this to happen after having the water pump changed but it seemed odd to me. Maybe the old water pump was inefficient and the new one had better pressure and caused anything close to failure to fail?

Anyways, I picked up a OEM oil cooler (she doesn't have DSG so one less thing to worry about) as dismantling the car, testing a part, ordering a part, waiting for it to arrive didn't seem like a good use of time. I then fitted it and flushed out the coolant system, replaced the oil and all has been good since. I never did test the old cooler, but seems to have been the culprit in my case. When you're pretty sure it's fixed you'll want to have the expansion tank off to give it a good clean, or order a new one, as the flush won't get the residue out of there.

In the back of my mind before and during the work was that it may be the head gasket, but as others say, these engines (Apart from the early BDK Diesels) are pretty much bullet proof when it comes to head/gasket issues and her's is the same engine they use for the 225 TT but is only running at 150, so I was fairly confident it wasn't that.

TLDR: It was the engine oil cooler and fixed for about £40 parts if I remember correctly.

Good luck

Stu

ricky:

--- Quote from: Stupots on September 11, 2020, 08:04:29 am ---I agree with both previous replies... plus, go for the cheapest option first, which is the engine oil cooler anyway.

If it's the same as an Audi TT (my girlfriends) then it's attached to the oil filter housing. Her's also got mayo/oil in the coolant which first appeared in the expansion tank following a timing belt and water pump change. Reading on various VWAG forums suggested it wasn't unusual for this to happen after having the water pump changed but it seemed odd to me. Maybe the old water pump was inefficient and the new one had better pressure and caused anything close to failure to fail?

Anyways, I picked up a OEM oil cooler (she doesn't have DSG so one less thing to worry about) as dismantling the car, testing a part, ordering a part, waiting for it to arrive didn't seem like a good use of time. I then fitted it and flushed out the coolant system, replaced the oil and all has been good since. I never did test the old cooler, but seems to have been the culprit in my case. When you're pretty sure it's fixed you'll want to have the expansion tank off to give it a good clean, or order a new one, as the flush won't get the residue out of there.

In the back of my mind before and during the work was that it may be the head gasket, but as others say, these engines (Apart from the early BDK Diesels) are pretty much bullet proof when it comes to head/gasket issues and her's is the same engine they use for the 225 TT but is only running at 150, so I was fairly confident it wasn't that.

TLDR: It was the engine oil cooler and fixed for about £40 parts if I remember correctly.

Good luck

Stu

--- End quote ---

That's interesting you say that as the car had a cambelt and waterpump change carried out recently.
SO maybe just that contamination. will flush the system and see if it goes away.
I hear the engine cooler is just a gaskit? and it labour intensive job?
Thanks for your help

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